Water-borne primer coating composition and method of forming coating film

A water-borne primer coating composition including a water-borne non-chlorinated polyolefin resin (A), a water-borne polyurethane resin (B), a water-borne epoxy resin (C) and an internally crosslinked acrylic particle emulsion (D),

• wherein the content of said resin (A) is 15 to 60% by weight,
• the content of said resin (B) is 10 to 50% by weight,
• the content of said resin (C) is 20 to 50% by weight, and
• the content of said emulsion (D) is 5 to 20% by weight
• on the solid equivalent basis in 100% by weight of the total amount of said resin (A), resin (B), resin (C) and emulsion (D),
• said resin (A) is a water-borne polypropylene resin having crystallinity of 35 to 55% and a weight average molecular weight of 50000 to 200000 and being converted to a water-borne resin without using an emulsifier,
• wherein the resin (A) is obtained by using a metallocene catalyst, and
• wherein the emulsion (D) is obtained by emulsion polymerization of a monomer composition including an ethylenic unsaturated monomer and a crosslinkable monomer, and
• a glass transition temperature of a non-crosslinked polymer obtained by polymerization of said ethylenic unsaturated monomer is 50 to 140° C., and
• the content of said crosslinkable monomer is 0.1 to 50% by weight in 100% by weight of said monomer composition.